NEW YORK (Reuters) - A U.S. unit of Mitsubishi UFJ Financial Group Inc is in talks to acquire the rights to sell trust-banking services to Morgan Stanley's clients, in the bank's latest bid to expand its business abroad, a source familiar with the matter said on Sunday.

The proposed deal involves Mitsubishi UFJ's Union Bank providing services to trust accounts worth an estimated $4 billion, which Morgan Stanley will continue to manage. Union Bank will earn fees on the trust services it sells, the source familiar with the matter said.